Telephone-exchange signaling circuit and apparatus



2 Sheets-Sheet 1.

(No Model.)

' T. N. VAIL.

TELEPHONE EXCHANGE SIGNALING CIRCUIT AND APPARATUS.

'n. PETERS. mwum w. WWW u a 2 Sheets-Sheet- 2.

(No Model.)

T. N. VAIL.

TELEPHONE EXCHANGE SIGNALING GIEGUIT AND APPARATUS. No. 274,857.

Patented Mar. 27,1883.

.Pruuento 7.

UNITED STATES PATENT" Orrrca.

'rrnnobonn N. VAIL, OF BOSTON, MASSACHUSETTS.

TELEPHONE-EXCHANGE SIGNALING CIRCUIT AND APPARATUS.

SPECIFICATION forming partof Letters Patent No. 274,857, dated March 27, 1883.

' Application filed December 18. 1882. (L o model.)

To all whom at may concern Be it known that I, THEO. N. VAIL, of Hos-- ton, in the county of Sufiolk and State of Massachusetts, have invented certain Improvements in Telephone-Exchange signaling Oircuits and Apparatus, of which the following is a specification.

My invention relates to the operation of telephone-exchanges or central-ofiice systems of telephonic intercommnnication, and particularly to the construction and arrangement of the apparatus at the substations and the central station of such exchanges with reference to the rapid and prompt disconnection of lines from one another upon the conclusion of a conversation.

Experience has demonstrated that it is desirable, in view of the fact that many calls have to be delayed on account of the line called for being already in use, that as soon as any line is disengaged the central station shall be enabled to readily ascertain its condition,so that thebnsiness of the otfice,whichis always heavy, may be accelerated.

The object of my invention, therefore, is to enable the. Supervising operator at the central station to become promptly appraised of the conclusion of conversation between any two sub-stations the lines of which have been conple act of replacing the telephone in its usual in certain instrumentalities, which are placed at each substation, and so adapted and arranged that upon the conclusion of a communication between any two Subscribers the simsupport shall operate to produce a certain abnormal condition in the main-line circuit; and i also in other and complementary devices placed at the central station, inconnection with and "forming a part of the said centrallstation apparatus, whereby the attendant by a simpleoperation is enabled to ascertain the condition of the main circuit, and consequently whether the conversation between the subscribers is or is not concluded.

In order to ascertain whether or not the conversation between any two subscribers has terminated, it has heretofore been customary to adopt one of three plans-either to retain the call-annunciator magnetof each connected line in circuit with the compound line formed of any two subscribers lines or to insert a special annunciator in the connecting-link between the two, whereby signals may be transmitted from the sub-stations to the central station in the same manner as the initial callsignal for interconnection was made; or to connect the two required lines together, leaving out the call-annunciators, and attach to any point on the connecting-link between the two lines a branch line to earth, including an annuneiator. When this method is adopted,and a signal is transmitted from either'terminal station, a portion of the signalingcurrent is transferred to the earth branch and passes off through the annunciator thereof, giving a disconnecting signal. Or to dispense altogether with any signaling device, whether looped into or branched from the combined circuit, and simply to connect the central-station telephone with the said combined circuit at occasional intervals, whereby the central-station operator is enabled to listen to any conversation passing and to disconnect the lines on the discontinuance of the same. Each of the foregoing plans has its disadvantages,which render their use more or less objectionable. The first plan adds to the electrical resistance and electromagnetic retardation of the line, thus deteriorating the quality of the transmitted art-icu lation S, besides depending for success upon the punctuality and reliability of the subscriber who is required to send the disconnecting sigand supervision of all connected lines, and entails much undesirable labor upon the centraloffice operator, and is also objectionable to the subscribers themselves, who prefer absolute privacy of communication. These practical disadvantages I aim to obviate by my invention.

In the drawings, vhich illustrate and form a part of the specification, Figure l is a diagram illustrating one plan of carrying out my invention, in which the replacement of the telephone brings into the line an electro-magnetic vibrator,which, on the application of a battery at the central station, becomes active, and rapidly makes and breaks the circuit. Fig. 2 repre-. sents a second plan, by which the replacement of the telephone greatly diminishes the line-re sistance, and by the consequent increase of the strength of current permits an electro-magnet at the central station to become vitalized. Fig. 3 is a detail of the device employed in Fig. 2 to loop in the battery and testing-instrument. Figs. 4 and 7 are modifications in which .the replacement of the telephone tends, by means of an electro-magnet and trip movement, to release a clock-work rotating a circuit-wheel, the said circuit-wheel intermittently making and breaking the main-line circuit. Fig. 5 is a detail of the hook-switch, and Fig. 6 an edge view of the circuit-wheel used in Figs. 4, 7, and 8. Fig. 8 is another modification, in which the central station is signaled and the circuit-wheel put in operation by a current derived from the central station itself. Fig. 9 is a front view of the circuit-wheel, and Fig. 8 shows a method by which the circuit-wheel is made to throw pulsations of electricity to line. I

In Figs. 1 and 2, 0 represents acentral telephone-station, ofwhich S is the switch-board. L and L are lines radiating from the switchboard to sub-stations A and B. It is well known that. in practice a great number of lines so radiate; but two are sufficient to exemplify my invention, and therefore to avoid complication in the drawings I haveshown but two. Entering each sub-station, the line runs first to the hook-switch F, its subsequent course depending upon the position of the said switch. The telephone, when not in use, is hung upon the hook, and by its weight brings the substance of the hook into contact with a contactspring, d which leads through wire 3,'signalbell D, wire 4:, elcctro-magnet 6, wire 6 armature f, back stop,f and wire 5 to the earth G,

the line being thus normally to earth through I the bell. When the telephone is removed from the hook, the hook, impelled by a retractingspring, (not shown,) flies up and makes contact with the upper spring, 0. This leads by wire 1, telephone T, transmitter T, and wire 2 to the earth. The two lines L and L are shown in Fig. 1 as being connected together on one of the horizontal bars a, of the centraloffice switch-board S for through oral communication. Each line is permanently connected at the central-office end with a vertical bar, I), and by insertingplugs p at the suitable intersecting points they may be united on any ofthe horizontal bars a, as shown. The horil when any of the keys are pressed, th may. 7 ture usually is retained against its back stop by its retracting-spring. It will be noticed;

that at each sub-station the bell-branch cir-i cuit is through the armature f and its back stop, f and therefore when any strong impulse; of electricity is passed through the electro-. magnetE the armatureisdrawnforward, break; f ing its own circuit, and consequently the ciri cuit of any line of which it forms a part.

The ordinary magneto-currents used in call-i ing are not sufficiently strong to afiect theelec-jl tro-magnet E. It is therefore ordinarily q-nii escentduring signaling and conversation; but

when two lines are connected, as in the draw-5 in gs, and the central-office operator desires to} ascertain whether the'conversation has con-l eluded, he presses the key It, connected with? that horizontal bar, and this operation con-i nects the battery M B and the electro-magnetl g, by means of the branch wire 6, with the pair:

of united line-circuits L and L. So long as the"; telephones at the two sub-stations are in use and the conversation is proceeding the only result at the central station accruing from the? pressure of the key is the attraction of the:

armature h by the magnet g, for the mere ad-;. dition of a battery-current to the telephone-f curret produces no apparent result; but if the conversation has concluded and the telephones have been hung up the bell branches. are both brought once more into circuit, and? with them the automatic electromagnetic cir-l cuit-breakers E, and upon the pressure of the;v

key is by the central-station operator the cur-i rent from the main battery M B traverses the,

lines in both directions, passing through the circuit-breakers E, causing them tov becomej operative and vibrate their armatures, at each I vibration breaking and closing the circuit on the back stop,f

The armature h of the central-office magnet is not provided with circuit-breaking points, but necessarily responds to the intermittent pulsations of electricity produced by thevibration of the sub-station circuit-breakers, and vibrates in correspondence therewith, whereby the central-office operator is apprised that the lines are to be disconnected,knowing that if the conversation is still in progress .his armature will the moment the key is pressed.

advarce only; but if the conversation has cona and as its cir f cluded the central-station armature will on At the central station one battery, blectromagnet, and armature may be common to a series of line-circuits, and be connected with each of the connection-strips a of the switchboard by means of branch wires and keys, as shown in the drawings. I also may unite the circuit-breaker E and bell D at each of the sub-stations in one instrnment,forming a vibrating bell.

.In Fig. 2, although I use the switch-board S at the central station and the hook-switch F at the sub-stations and connect the sub-stations and central station by line-wires L L, as in Fig. 1, the instrnmentalities which p31- ticularize my invention are somewhat different. and are constituted as follows: At each sub-station the bell branch 3, to which thelineis normally, by the depression of the hook-switch under the influence ot' the telephone, united, includes only the signal-bell l), the circuitbreaker E being omitted. The telephone branch, to which the line becomes united by the elevation of the hook-switch when relieved from the weight of the telephone, includes, in addition to the usual 'telTephone, T,

andtransmitter '1, a rheostat or high resistance, I. This may be adjustable, or may be of a constant magnitudefor example, ten thousand ohms. This I bridge by a condenser, H, so that the rhythmical pulsations of electricity, by which articulate speech is reproduced, will not be impeded by having to pass through the rheostat, it being well understood by those skilled in the art that the said rhythmical impulses are readily transmitted through a condenser by induction. By the united use of these instrumentalities I maintain a very high resistance in the talking-circuit, and at the same time prevent that resistance from diminishing the sound of transmitted speech.

.At the central station, in convenient proximity to the switch-board S, I place two parallel bars,j and j, one of which, j, is connected by a wire, 17, directly with one pole of a battery, M B, while the other bar, j, connects by wire 18 with the other pole of the battery, after passing through the electro-magnet g. Arranged between this airot' parallel strips I place a series of spring-jacks, of the character delineated in Fig. 3, each consistin g of a pair of leaf-springs, Z l, and normally pressing against one another. One spring jack is alloted to each pair of the connectionbars a in'the switch-board S, and each of the said switch-board bars is permanently con-' nected by a wire with one of the springs of one of the spring-jacks. In the drawings it will thus be seen that of the uppermost pair of bars,a a, a. is united by wire 13 to spring Z of its own jack, while a is similarly united by wire 14 to the spring I, which normally presses against the spring 1, making contact therewith, the two jointly constituting the spring-jack. In connecting any two lines together in this system I use'a pair of connection-bars, (1, instead of one, as in Fig. 1, and when any two lines are connected for inter communication theircourse through the switchboard is thus traced: From line L to vertical bar I), and by plug 12 to cross-bar a, and by wire 13, spring l of the spring-jack, thence by contact between the springs to l, and by wire 14, horizontal switch-bar a',.plug 19, vertical switch-bar b, and thence to line L. The two parallel bars j and j form the normally-open terminals of the battery M B, and have no contact with any circuit until the two springs of the spring-jacks are forced apart by inserting a suitable wedge, m, between them. When this is done the outside surfaces of these springs make contact with the bars j, thus looping the battery M B and magnet-coil ginto any two lines which may at that time be connected with the spring-jack. When the apparatus at the central and sub stations is arranged as hereinbefore described, the state of the line may be ascertained at once by pressin ga wedge between the jack springs of the required line. This may be done by arranging over the several jack-springs a key-board and a set of press-keys, which, when pressed, will insert a wedge, as described. It theline is in use and the sub-stations are conversing, no effect will be made manifest on the central-office instruments, because the rheost-ats at each of thesubstations are in circuit, and their resistances are so great that the battery-current is materially weakened, and has no power to attract the armature of the electro-n1agnet g; but if the conversation is concluded and the telephones are in place the rheostats are cut out, the resistance of the line reduced to its normal condition,and the battery-currentis sufficiently strong to actuate the testing-magnet g. In this case, then, the operator knows the instant that he inserts the wedge m, and thusintroduces the battery into the circuit, that if his testingmagnet responds the con versation is concluded,

and that he may disconnect the lines, and that if the testing-magnet does not respond the conversation is not concluded, and that more time is required.

In the plan which I show in Fig. 4.- the central-station devices may be identical in character with those shown in Fig. 2; and I may here state that although I have represented the electromagnetic device at the central station to besimply an electromagnet and armature any other instrument, as an electric bell or annunciator, may readily be substituted therefor.

I will now describe the sub-station arrangement shown in 4.

F is the hook-switch, which carries two flat contact springs, 10 and 11, the former being electrically connected with the metal hook and the latter insulated therefrom.

On the inner side of the hook-lever, and affixed thereto, but

insulated therefrom, is a second metal bar, 1?,

ill I I llll terminating also in a hook which coincides in position with the main hook, as shown in Fig. 5. The incoming line is united with the spring 11, and, as usual, when the hook is depressed and the telephone hanging thereon, is connected with earth through a signal-bell. When the telephone is removed the hook transfers the line to a second branch leading through the telephones to earth.

A circuit-wheel, 0, having, 6, one conducting-plate, p, pletely across its periphery, and a number of others, p partly across, is suitably arranged to rotate by means of a clock-movement when released, and through the broad contact-piece or conducting-plate p the bell-branch circuit is led, and may-be traced, via hook -contact 13, wire 5, contact-sprin g 7, wheel-plate 10, contact-spring 8, wire 6, bell D, and ground-wire 2. Thetclephone-branch leads directly through as shown in Fig. stretching comthe telephone T and transmitter T to earth from the hook-plate 12.

A local battery, L B, which in practice may be the transmitter-battery, has one of its poles connected with the ground by a wire, 2, the same pole being also united by wire 3 with the plate 9 above the hook. The spring 10 slides over the plate 9, makin g frictional contact therewith when the hook moves up or down.

Attached to the auxiliary hook F (see Fig. 5) is a wire, 1, which leads to one terminal of an electro-rnagnet, E, issuing from the other terminal thereof. The circuitproceeds through the armaturelcverf and the detentf, which projects from the rear of said lever. to the pin '22; which is inserted in'the side of the circuit- Wheel 0, from whence it continues, by means of the radial wire y, to the arbor m of the wheel, and from there, by the contact-sprin g f, which bears on the said arbor, and the wire 21, back to the other pole of the local battery. The local-battery circuit is normally open at the plate 9, and may be also opened at the book, where, when the telephone is in place, it is completed by the telephone-ring. it may also be opened between the point 11 on the circuitwheel and the projecting detentft In practice the spring 7, pressing on the edge of the circuit-wheel, is fixed in front of the spring 8, as shown in Fig. 6, and as soon as the rotation of the wheel commences the spring 7 only makes contact with the intermittent metallic plates, the spring 8, connected with the signal-bell, being thus insulated and pressing on the non-conducting substance of the wheel until the rotation of the wheel has concluded, and both springs once more rest upon the plate 20', which is common to both.

The operation of these devices may bedescribed in the following manner: When the telephone is on the hook the ring by which it hangs makes the electrical connection between the two books F and F and the line is complete through the signal-bell line to earth. When a call is received and the bell D rings the subscriber takes his telephone from the hook, which flies up until the spring 11 rest? on the plate 12,

thus connecting the main lini through the telephones to earth. As the 160311;

circuit is opened by taking the telephone from the hooks, and thus removing .the electrica connection between the hooks F and F ant before it can close by contact between the springs 10 and plate 9, the electro-magnet 13 remains inoperative; but when the converse? tion is concluded and the telephone is replaced the local circuit is once more closed between negative pole of the battery. The magnet 11),:

bein thus energized attracts its armature;

which withdraws the detent from the pin 0,1; whereupon the wheel, propelled .by a suitable:- rotates its alternate conducting clock-train, I I and non-conducting spaces, passing'under the? spring 7, leading to the line and central sta-ftion, andv by means of the ground-wire 2, at-;? electrical impulses are sent over the line to the central station route: ground-wirez, 'batspring f arbor w, radial wires and conducting-plates p contact-f tached to the local batter over the following tery L B, wire 21,

spring 7, wire 5, plate 13, spring 11, and lineii L. These pulsations are, owing to the charactor of the circumference of the wheel, in ter-Jt mittent. and when the central-office operator presses his key or inserts his wedge, as intFig. 3 2, he at once becomes cognizant that the line is now disengaged, because his testing-instrument so indicates by its successive and inter-' mittent movements. If that instrument be a telephone, he also understands thecondition f of the line instantly, at once to electrical ture.

The circuit-wheel is so arranged with repower as to be capable of adjustment to any desired rate of speed, and such a rate as would produce one revspect to its motive I: prefer as a telephone resp0nds changes of whatever naolution of the wheel in about five minutes. The alternate conducting and non-conductin g 'j spaces upon the edge of the wheel may be of any desired number, but I have for the sake of olearness in the drawings refrained from showing a large number.

If a battery is arranged at the sub-station, as in Fig.4, to send successive pulsations toward the central station, no battery willbe required at the central station, but a testing-instrument only. f

In Fig. 7 I present a modification of the plan described in Fig. 4, in which the local, battery L B has no ground branch. The circuit-wheel, therefore, instead of sending electrical' impulses to the line and toward the central oflice, merely has the function of alternately breaking and making the line-circuit, and the presence of the central-office battery is an essential in the operation of this plan.

. Fig. 8 represents still another modification in the details of the plan described fully in I Fig. 4:, in which I show my invention operated in connection with the system of automatic plate p on the circuit-wheel, and by means of the contact-spring 11 the line isbrought into connection at the ends of its up-and-down movement with these branches. The local circuit, by which the tripping of the circuit-wheel mechanism is efi'ected, is led through the contact-plate 9 and spring 10 and through the two hooks, but not through the armature-lever f of the electro-magnet E. Hence the sole office of the local circuit is when closed to energize the helix 0 of the magnet E on the down movement of the hook-switch, and thus trip the circuit-wheel. Between the terminal plates 12 and 13 of the telephone and bell branches is a third contact-plate, 20. This is connected by a wire, 4, with the spring f that presses on the arbor of the circuit-wheel O, and by the radial wires y also with the conducting-plates 19 which are let in on one side only of the edge of the wheel. The plate 20 is also connected by a branch wire, 22, with an electrical-supply circuit, g, which, in accordance with the patcut I have hereinbefore cited, is constantly charged by a source of electricity, preferably located at the central station. This supplywire is common to a number of sub-stations, which it enters by branch circuits 22. It is obvious that as the hook-switch F descends under the weight of the telephone or rises when the telephone is removed, the spring 11, while in transit from the bell-branch plate 13 to the telephone-branch contact-plate 12, or vice versa, must pass over the intermediate plate, 20, coming into frictional contact therewith. As it passes upward the only result is to place the main line L in momentary connection with the constantly-charged plate 20, and thus to send a pulsation of electricity to the central station over the main line to give a signal at the central station. As the hook passes downward a second momentary signal is given, followed by successive signals produced by the rotation of the circuit-wheel, this being, as hereinbefore described, tripped only during the downward movement of the hookswitch. While the wheel is in rotation the normal ground terminal of the line L is removed, the spring 8 rubbing on the non-conducting periphery of the wheel only, and the said line is, by means of the spring 7 and the alternate conducting-plates p of the wheel, brought into intermittent contact with the charged supply-line, whereby the electrical impulses continue to go to line during the rotation of the wheel, and when the said rotation is concluded the earth-connection through the bell branch is restored.

In Fig. 8 another method is shown, in which a contact-sprin g, P, connected with a main line, is acted upon by the spokes ofa rotating wheel, W, which places the said spring in in termittent contact with a battery, L B.

In Figs. 7 and 8 lhave not thought it necessary to show the telephone-instruinents,and have merely indicated them.

Having now fully described my invention, I claim- '1. In a telephone-exchangesystem,thecombination of a central station, a series of substations, a line connecting each sub-station with the central station, automatic devices at the sub-stations whereby the electric condition of the line is altered at the close of a communication,- and a test apparatus at the central station which indicates upon the depression of a key or by equivalent means, as specified, whether the communication is at an end, substantially as described.

2. In a telephone-exchange system comprising a central station and a series of sub-Sta tions, the combination of a signaling device at the sub-stations automatically brought into operation by the switch-hook in hanging the telephone thereon, and a testing device at the central station, which upon being applied by the operator indicates whether or not the telephone at the sub-station has been restored to its hook, substantially as described.

3. The combination, with devices at the substation, brought into operation by the movements of the telephone book when the telephone is replaced thereon to change the electric condition of the line, of testing apparatus at the central office, comprising a local battery, means for closing the same, and an indicatin g device, which, when the-circuit is closed by the operator, shows whether the telephone has been replaced upon its book, substantially as described. 1

4. The combination, at a sub -station in a telephone-exchange system, with the mainline, the signal-bell and telephone branchlines, and an automatic switch actuated by the removal and replacement of the telephone to place the said main line in electrical connection with either of said branches, of a rotary intermittent circuit-changer, a local battery and circuit controlling the movements of the same, and a circuit-closer operated by the automatic switch in the said local circuits, and adapted to become operative only during the movement of the said automatic switch from the telephone to the bell branch, whereby when the telephone is put in place on the conclusion of acommunication the rotary circuit-changer is actuated and continues to close and break the mainline ICC IIS

circuitorto transmit electrical pulsations over the main-line circuit for a definite period, substantially as and for the purpose set forth.

5. In a telephone-exchange system,the combination, substantially as hereinbefore described, with amain line, of the signal-bell and telephone branch lines, an automatic switch actuated by the removal from or replacement of the telephone in its support to place the said main line in contact with either of said branch lines, a rotary intermittent circuit-changer, a local battery and circuit controlling the movements of the same, a circuit-closer in the said local circuit operated by the automatic switch, and adapted to become operative during the movement of the said automatic switch from the telephone to the bell branchall at each sub-station, and of an electro-magnetic testinginstrument, and devices for connecting th esaid instrument with any pair of interconnected lines at the central station, whereby when the telephone is replaced on the conclusion of a communication the rotary circuit-changer is actuated and continues to change the electrical condition of the main-line circuit for a definite period,and whereby the said changes may be noted at the central statiomas described. 6. The combination, substantially as hereinbefore described, of a local battery andcircuit, a rotary circuit changer, an electro magnet,

armature, and armature-lever controlling the same, all in the said local circuit, 'a leverswitch forming a support for the telephone when inplace, and consisting of two parallel hook-levers attached to but insulated from one another, and each forming a portion of the local circuit, a metal telephone-ring, by which the telephone is suspended from the said hooks,

and which, when the telephone is in place, con-' but operative when the telephone is replaced,

whereby the action of replacing the telephone closes the local circuit, energizing the electromagnet and permitting the rotation of the rotary circuit-closer, as described.

In testimony whereofl havesigned my name to this specification, in the presence of two subscribing witnesses, this 14th day of December, 1882. p

THEO. N. VAIL.

Witnesses:

GEO. WILLIS PIERCE, Tnos. D. Locxwoon. 

